Re: [PATCH] Rework dev_base via list_head

[David Miller <davem@davemloft.net>]

From: Pavel Emelianov <xemul@sw.ru>
Date: Wed, 02 May 2007 17:40:56 +0400

> Cleanup of dev_base list use, with the aim to simplify making
> device list per-namespace. In almost every occasion, use of
> dev_base variable and dev->next pointer could be easily replaced
> by  for_each_netdev loop. A few most complicated places were
> converted to using first_netdev()/next_netdev().
> 
> Fits 2.6.21-rc7 tree.
> 
> Signed-off-by: Pavel Emelianov <xemul@openvz.org>
> Acked-by: Kirill Korotaev <dev@openvz.org>

Overall this looks mostly good.

One thing I want to audit before applying this is
loop termination conditions.

With the old loop, if you do something like this:

	for (dev = dev_base; dev; dev = dev->next) {
		if (dev == what_I_want)
			break;
	}

you can test for a successful find after the loop with:

	if (dev) {
		I_found_it();
	}

That doesn't work with for_each_netdev(), if the loop
runs till the end of the list, the iterator will not
be left at NULL.

I just want to make sure you didn't leave any code around which wants
that behavior still.

This is one of the subtle things about using the list iterators in
linux/list.h, vs. a traditional by-hand singly linked list
implementation.